The present application relates to a technical field of a seat belt retractor, for retracting a seat belt such that the seat belt can be freely withdrawn and wound, in a seat belt apparatus installed in a vehicle.
More particularly, the present application relates to a seat belt retractor that comprises a seat belt load limiting mechanism for absorbing an occupant's kinetic energy to limit load on a seat belt at the time of preventing seat belt withdrawal in the event of an emergency such as a collision in which a large deceleration acts on a vehicle when the occupant wears the seat belt, and a seat belt.
Conventionally, a seat belt apparatus installed in a vehicle such as an automobile restrains an occupant with a seat belt in the event of an emergency as mentioned above. Such a seat belt apparatus is provided with a seat belt retractor for winding up the seat belt. In the seat belt retractor, the seat belt is wound onto a spool when the seat belt apparatus is not used and is withdrawn from the spool to be worn by the occupant when the seat belt apparatus is used. The seat belt retractor has a locking mechanism which is activated in the event of an emergency as mentioned above to prevent the spool from rotating in the seat belt withdrawing direction, thereby preventing the withdrawal of the seat belt. Therefore, the seat belt securely restrains the occupant in the event of an emergency.
In the seat belt retractor of the conventional seat belt apparatus, the occupant is forced to move forward by a large inertia force because of large deceleration acting on the vehicle when the seat belt restrains the occupant in the event of an emergency such as a vehicle collision. Accordingly, a large load is applied to the seat belt by kinetic energy of the occupant and the occupant thus receives a large force from the seat belt. It is preferable to reduce the force applied to the occupant.
For reducing the force, a variety of seat belt retractors with seat belt load limiting mechanism have been developed. The seat belt load limiting mechanism may include a torsion bar and a shear pin as a shearing member which are disposed between a spool for winding up a seat belt and a locking plate for locking the rotation of the spool in the belt withdrawing direction.
One seat belt load limiting mechanism includes an energy absorbing mechanism (hereinafter, sometimes referred to as “EA mechanism”) that absorbs kinetic energy of the occupant by torsional deformation of the torsion bar and the shear deformation of the shear pin when a relative rotation is generated between the spool and the locking plate (e.g., in the event of an emergency when the seat belt is worn). The kinetic energy of the occupant is absorbed by the EA mechanism, thereby limiting the load on the seat belt. The load reduced by energy absorption of the EA mechanism is an EA load and is a limited load indicating the limited amount of load acting on the seat belt. The shear pin is fitted in an axial hole of the spool. Accordingly, as the shearing load acts on the shear pin during the relative rotation between the spool and the locking plate, the shear pin moves in a direction coming off the spool. However, a portion of the locking plate where the shear pin is fitted moves apart from the spool to create a space between the locking plate and the spool so that a bending load also acts on the shear pin in addition to the shearing load.
It would be advantageous to provide a seat belt retractor with a load limiting mechanism that limits a bending load acting on a shearing member and to provide a seat belt apparatus employing the seat belt retractor.